In patent application Ser. No. 311,063 entitled "Recovery of Metal Values from Manganese Deep Sea Nodules", filed on Dec. 1, 1972, by Lester J. Szabo, the teachings of which are incorporated herein by reference, a process is disclosed in which copper, nickel, cobalt and molybdenum are recovered from raw manganese nodules with an aqueous ammoniacal leach solution containing cuprous ions. The process disclosed in application Ser. No. 311,063 is a significant breakthrough in the metallurgical art in that it significantly expands the world's source of copper, nickel, cobalt and molybdenum. The process disclosed in application Ser. No. 311,063 has come to be called the "cuprion" process. The cuprion process includes the step of contacting ground manganese nodules with an ammoniacal leach solution containing cuprous ions in a reaction vessel to reduce the manganese oxides in the nodules to enable metal values such as copper, nickel, cobalt and molybdenum to be solubilized. The leaching produces a leach slurry which contains reduced solid nodules with entrained metal values as well as dissolved metal values. The solid nodule residue is separated from the liquid and the liquid is recycled. The nodule residue is washed with an ammoniacal ammonium carbonate solution to remove entrained metal values from the residue. Thereafter, the metal values are extracted from the wash liquor.
The leach slurry is solid MnCO.sub.3 with some Fe(OH).sub.3 and clays, and liquor consisting of an NH.sub.4 OH -- (NH.sub.4).sub.2 CO.sub.3 solution containing solubilized copper and nickel with lesser amounts of cobalt and molybdenum values. The cuprion process normally uses a countercurrent wash circuit consisting of seven thickeners, to wash the solids of entrained metals. Of course, large capital expenditures are required for the wash apparatus and the apparatus is relatively costly to operate.
In the wash circuit of the cuprion process, slurry containing about 45 percent by weight solids is contacted with with NH.sub.4 OH -- (NH.sub.4).sub.2 CO.sub.3 solutions through various wash stages at a wash ratio of about 2 to 1. Pregnant wash liquor is contacted with an organic extractant to recover copper and nickel values. The raffinate is steam stripped and treated to remove cobalt and molybdenum.
Direct extraction of metal values with the organic from the nodule slurry would eliminate the washing circuit with a large attendant capital savings. It would have the further advantage of greatly decreasing plant space requirements, therby making it possible to perform shipboard processing of nodules.
This invention relates to the separation and recovery of desired non-ferrous metal values from a slurry of solids and solution which contains such metal values. In a broader sense, however, this invention is an improvement in extraction leaching and can be used to great advantage in any leaching process. The direct extraction of leached metal values from slurry is a desirable step in many commercial operations. Extensive prior art studies have been performed on resin-in-pulp extraction using ion exchange beads and screens to separate them from slurry particles. A major problem in the process is the attrition of the resin beads and the attendant expense of their replacement. The process has been used commercially only for expensive metals like uranium.
Solvent-in-pulp processes have been explored using different types of contactors. Entrainment losses of organic are invariably high and increase with the degree of agitation, and there is a great tendency to emulsion formation. Organic losses are also dependent on the adsorption of the liquid ion exchange reagent on the particles in the pulp. Commercialization of this technique has not been realized.
In short, for the past ten years, work has been in progress to improve the economics of recovery from leached ores by direct solvent extraction of metal values from a slurry. However, a method for directly leaching base metal values from slurries which could be used on a commercial scale has not materialized.